1. Field of the Invention
The present invention relates to tactile feedback and, more particularly, to an apparatus and method for providing detent-like tactile feedback.
2. Description of the Related Art
Detent mechanisms are typically found on the shafts of rotary volume or channel selector switches such as, for example, those found on some televisions and radios. Such detent mechanisms are also used on the horizontal and vertical deflection factor controls on oscilloscopes and similar instruments.
FIG. 1A illustrates an example of a detent mechanism used on a conventional rotary switch. As shown, cam 1 includes a number of valleys 4 and hills 5 and is capable of rotating about shaft 7 in the directions indicated by arrows A. A spring loaded pawl, referred to generally as pawl 6, typically consists of a leaf-spring 3 and a ball bearing 2, with leaf-spring 3 urging ball bearing 2 toward cam 1. As cam 1 is rotated, pawl 6 causes cam 1 to favor a position at rest in which ball bearing 2 is positioned in one of the valleys 4. This type of detent mechanism offers a restoring force (e.g., a force opposite to the displacement of cam 1) when attempting to leave one of the stop positions in one of valleys 4. The effect is to guide the user's hand to a valid switch stop position.
Another mechanism that has been employed to obtain a detent action is illustrated in FIG. 1B. Ferro-magnetic spur wheel 12 includes spurs 13 and is rotatable about shaft 14 in the directions indicated by arrows B. A magnet 11, including south (10A) and north (10B) poles is provided in proximity with wheel 12. Due to magnetic action, the mechanism remains at rest when spurs 13 of spur wheel 12 are aligned with poles 10A and 10B of magnet 11. This type of detent mechanism also offers a restoring force when attempting to leave one of the stop positions.
Although such detent mechanisms may be suitable for use in rotary switches, such mechanisms have limited use for other applications requiring more than one degree of freedom. For example, it may be helpful to provide a detent mechanism on a cursor positioning device such as a track ball or mouse-like device to obtain a precise position of the cursor on a video display. However, one disadvantage of using the above-described mechanisms in a track ball or a mouse-like device which utilize movement of a ball to position the cursor, is that physical hills and valleys (or spurs) must be provided on the surface of the ball, to obtain the desired detent action. However, neither hills, valleys nor spurs may be employed on the surface of the ball, since the ball must be able to roll (in place) with ease in any direction. Hills or spurs on the surface of the ball would prevent continuous and straight movement of the ball. Small dimples on the surface of the ball may provide a solution. However, with the dimples affixed to the track ball the available stop positions and the directions to them are also fixed to the pattern of dimples, with the possibility of yielding no continuous "straight" paths. In addition, with the ball free to rotate with compound motions, the direction to the next detent stop position will keep changing.
An attempt has been made at providing a tactile feedback in a mouse-like input/output device. For example, U.S. Pat. No. 5,186,629 has addressed a tactile feedback that is sent to a mouse-like input/output device. The device is intended to provide computer output to blind computer users to visualize computer graphic images. In particular, a determination is made if an object has been located, by providing feedback to the mouse when a boundary (e.g., a boundary of a window or an image) is encountered. The feedback is in the form of a mild electrical impulse or a physical vibration. However, although this device may be useful to alert a user when a boundary is encountered, it is not particularly useful for providing a detent-like physical tactile feedback having dragging and/or restoring forces. That is, the above-referenced device does not provide a detent-like sensation similar to the sensation received using a physical cam and pawl.
Attempts have also been made at simulating detent action. For example, U.S. Pat. No. 5,204,600 relates to an apparatus and a method for simulating a mechanical detent in a manually operable rotary digital encoder used to control a display or a readout in an electronic system. In particular, the apparatus simulates tactile feedback of a physical detent by temporarily freezing the encoder output to the display or readout, when the encoder is rotated past a virtual preset point (e.g., a stop position). When the user rotates the encoder past the preset point, the system engages a time delay, during which the output from the encoder to the associated electronic system is maintained at the preset point value. The delay allows the user to stop the movement of the encoder to achieve a desired preset point value. However, even though this method and apparatus may be useful in achieving a virtual preset point value utilizing a display or a readout, the method is not particularly useful to obtain a periodic, physical detent-like tactile feedback.
Accordingly, it would be beneficial to provide a detent-like tactile feedback in a track ball-like or mouse-like input/output device.